An integrated circuit structure includes a gate stack over a semiconductor substrate, and an opening extending into the semiconductor substrate, wherein the opening is adjacent to the gate stack. A first silicon germanium region is disposed in the opening, wherein the first silicon germanium region has a first germanium percentage. A second silicon germanium region is overlying the first silicon germanium region, wherein the second silicon germanium region has a second germanium percentage higher than the first germanium percentage. A metal silicide region is over and in contact with the second silicon germanium region.